It is state of the art to clean hard surfaces such as metal or non-metallic surfaces, e.g., building walls or ceramics, with abrasive agents. This is carried out for reasons of hygiene or in order to prepare surfaces for a protective coating. The aim of the cleaning composition is to remove, from metallic and non-metallic surfaces, the mineral, vegetable and animal oils, fats, waxes and soiling and other inorganic and organic compounds and salts, such as ash, powders, granules, dusts, pigments, fillers, soot, tar, organic polymers and the like which adhere thereto.
Cold cleaners are used to detach contaminants of the above-mentioned type from hard surfaces and to transfer them into the aqueous phase. Requirements placed on environmentally-friendly cold cleaners of the first generation were rapid dissolution and detachment of the soiling and rapid separation of the oil and solvent phase from the aqueous phase and low solubility in water of surfactants, emulsifiers and solvents. The second generation, the group of rapidly separating cold cleaners, is based on surfactants or surfactant mixtures which form coarsely disperse water-in-oil emulsions which also break down relatively quickly. Environmentally friendly cold cleaners of the third generation use organic salts, which, because of their chemical structure, have a high affinity towards hard surfaces. Layers of soiling are undermined over their whole area, resulting in virtually complete removal of the soiling upon subsequent cleaning with water. The effectiveness of a cleaning composition is determined by its ability to wet and penetrate soiled surfaces, and thus to promote solubilization and dispersion.
The ability of a cleaning composition to be effective is thus a combination of a number of effects, namely lowering of the interfacial tension between an aqueous and an oily phase and influence of the interaction between particles and wash liquor as a result of penetration and salvation, association, absorption and hydration.
The technical solution to this problem usually involves using processes which spray abrasive cleaning compositions under high pressure. This can be carried out using an aqueous solution, suspension and dispersion of the cleaning composition or a suitable mixture of cleaning compositions with or without carriers. Also known, from U.S. Pat. No. 4,817,312, incorporated herein by reference in its entirety, are dry processes, i.e., processes which use compressed air, or combinations of dry ("sandblasting") and wet blasting techniques.
In low-pressure processes of U.S. Pat. No. 5,487,695, incorporated herein by reference in its entirety, the formation of large amounts of dust is avoided by mixing water and compressed air in the nozzle and so limiting the formation of soiling during use by means of a particular nozzle technology.
A frequently used method for the abrasive cleaning of surfaces is the sandblasting method. Sand is a very hard abrasive material which can be used effectively for removing paint or encrustations on metallic surfaces, such as steel. Although silicates are very useful for all types of abrasive blasting techniques, they also have some serious disadvantages.
A health risk for an operator is that microcrystalline silicate fractions which form as a result of silicate crystals being crushed on the surface to be cleaned can pass into the lungs and thus lead to serious health problems. In particular, the expenditure for cleaning the surrounding area when sandblasting is complete must be taken into account. For many surfaces, sand is too hard a material which permanently damages the structure of the surfaces to be cleaned, for example, in the case of aluminum, plastics surfaces or wood. In the industrial sector, sand can enter machinery and can permanently damage engines and mechanisms.
For this reason, pressurized jet cleaning using sodium bicarbonate has been developed as an alternative to the silicate process. U.S. Pat. No. 5,081,799, incorporated herein by reference in its entirety, and U.S. Pat. No. 5,083,402, incorporated herein by reference in its entirety, disclose the use of abrasive agents instead of sand, such as sodium chloride or sodium bicarbonate. Sodium bicarbonate is usually blasted onto the area to be cleaned at superatmospheric pressure with or without the addition of water. Here, the sodium bicarbonate crystals clean, firstly, in an abrasive manner, i.e., physically. Secondly, they provide a chemical cleaning power since, as a result of their alkalinity, they are also able to attack in a chemical manner and hydrolyse. It is likewise possible to use SiO.sub.2 -hydrophobicized particles (WO 91/15 308, incorporated herein by reference in its entirety) of inorganic salts, which significantly reduce the hygroscopicity of many salts and thus permit better industrial application because clumping in the high-pressure plant is largely suppressed. Sodium bicarbonate is not harmful to the environment and is readily soluble in water, meaning that any crystalline particles which remain can be washed away with water (U.S. Pat. No. 5,487,695, incorporated herein by reference in its entirety).
A common characteristic of all of the processes described in the prior art and established in practice is that, irrespective of how the abrasive cleaning of surfaces is carried out in technical terms and irrespective of the abrasive materials and cleaning compositions used therefor, they must always be followed by a second, labor-intensive cleaning process. This shortcoming means that the soiling which has been removed and the spent cleaning composition must be cleaned away together, or sedimented solids must be collected and disposed of by other suitable measures. It is thus considerably time-consuming and costly to likewise have to post-treat and clean the area directly surrounding the cleaned area.
The object of the present invention was thus to undermine, dissolve, detach or rub down deposits of the above type using suitable cleaning compositions, and to disperse and stabilize the soiling in an iso- and a polydisperse manner, as finely as possible, in the wash liquor. The aim in particular was to largely suppress sedimentation processes in the wash liquor in order to be able to dispose of the liquor with as high a soiling content as possible directly in an environmentally friendly manner, thus satisfying the desired application requirements with regard to dispersibility of the waste water. In this way, the expenditure on post-treatment and cleaning of the surroundings can be eliminated or at least be considerably reduced.
At the same time, the known advantages of cleaning with sodium bicarbonate should be retained. The main advantages are the positive ecological properties of the material, its good cleaning action and solubility in water, and comparatively low health risk for the user. Moreover, appropriate choice of the pressure range allows the abrasive action of the material, which is in some cases hydrophobicized, to be influenced such that the structure of the surface to be cleaned remains undamaged.